Just a heads up: TinyUmbrella has been updated to version 5.00.07. This new version supports iOS 4.3.5 and has the option for restoring/updating the iPhone 4 baseband. It’s important to read what Notcom had to say about this update below:

I’ll probably regret this but this newest version of TU (5.00.07) will allow you to choose whether or not to update your iPhone 4’s baseband. This new feature comes with a catch:

First, the version you WANT to restore to and the version Apple is currently signing must BOTH have the same baseband. This is important or else the baseband update will not work and you will get a 10xx error and need to use fixrecovery. (Works for iPhone 4 – will not work for iPad 2)

Second, you need to realize that checking the box WILL UPDATE YOUR BASEBAND.

Third, I’m working on a simple tool that will allow you to create a pseudo-custom firmware mixing a new baseband with an older iOS version (one that is jailbreakable for example). This feature exists in the TinyUmbrella rewrite but does not yet exist in the older codebase. SORRY! I’m working on it!

I do not save your ‘UPDATE iPHONE 4 BASEBAND’ setting. If you wish to restore while updating/restoring your iPhone 4 baseband you must check that box every single time you run TinyUmbrella. It is just safer that way.

Also, iPad 2 users can still restore to 4.3.3 if they have their 4.3.3 SHSH. Just ‘Start TSS Server’ and then start up iTunes and restore your 4.3.3 ipsw. TinyUmbrella should help you restore without a 10xx error.